Diamondback rm 20 kids bike. Can you adjust the handlebars?

Looks like there's a push on plastic cover on the handlebar head stem. Gently pry the cover out and there will be a bolt underneath it (most likely an allen key/hex key bolt). Loosen the bolt and wriggle/twist the handlebars while adjusting the height of the bars. There will be a minimum insertion line on the shaft of the head stem - do not adjust the height above that line or there will not be enough of the shaft to lock into the front forks. Make sure that bolt is tightened up very firmly once you've made the adjustment and reinstall the plastic cover.

Robert, Below I have posted links showing how to adjust handle bar height for most, some bikes bars are not adjustable and are welded. If the links do not help I suggest you do a google search. Check the attached links,instruction and guides, Good luck
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I'm answering 7 years later. I have a Schwinn Varsity 2500 Bike made probably in 2015. The Schwinn Varsity Bike is not set up the same way as a traditional bike. I loosened the center compression bolt and the two side stem clamp bolts and it came loose where I can adjust it up or down but, there's nothing to tighten the slack up below. I did some research. My original post here was to add or remove a spacer. I think you can remove a spacer to lower but, I don't think the stem is long enough to add another one. I've seen they sell an extension that you can add-on to make the handle bars higher.

Web search teh question "How do I raise the handlebars".

A major limitation is the steerer tube length. No matter how many times you cut a steerer tube it won't get longer.

Getting Riser Bars or simply flipping the stem over or getting one with a different rise and reach might give you the added height you need. If you LIKE the handlebars, the stem is the best and least-invasive option as most new ones come with front loaders (detachable front caps) that allow replacement without stripping components off one side of the handlebar. In minutes a Bicycle Shop could swap any number of them onto your bike for you to try.

If you had purchased the bike at a reputable Bicycle Shop they would have fit the bike to you before you took it home.

http://www.sheldonbrown.com/handsup.html

A major limitation is the steerer tube length. No matter how many times you cut a steerer tube it won't get longer.

Getting Riser Bars or simply flipping the stem over or getting one with a different rise and reach might give you the added height you need. If you LIKE the handlebars, the stem is the best and least-invasive option as most new ones come with front loaders (detachable front caps) that allow replacement without stripping components off one side of the handlebar. In minutes a Bicycle Shop could swap any number of them onto your bike for you to try.

If you had purchased the bike at a reputable Bicycle Shop they would have fit the bike to you before you took it home.

http://www.sheldonbrown.com/handsup.html

Getting Riser Bars or simply flipping the stem over or getting one with a different rise and reach might give you the added height you need. If you LIKE the handlebars, the stem is the best and least-invasive option as most new ones come with front loaders (detachable front caps) that allow replacement without stripping components off one side of the handlebar. In minutes a Bicycle Shop could swap any number of them onto your bike for you to try.

Do you mean the stem is allowing them to twist? THAT is a dangerous situation and you should get a real competent Bike Shop, not just a dealer, to look it over. If the tighening bolts are bottomed out it won't hold tight. Or if one side is bottoemd and the other gap is wide.

Using this picture as a general guide since it might not match your stem...

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=280652429524&clk_rvr_id=242489366593&item=280652429524&lgeo=1&vectorid=229508

The gaps should exist and be even. Not metal to metal. Handlebars and stems come in different diameters. Perhaps yours are incompatible.

The handlebars are in a fixed position, they cannot be raised.

some bikes u cant only the seats can adjuct